Language immersion elementary

Has anyone taken language immersion classes?

They offer language immersion school where most children will learn a new language the school will be in a foreign language

My concern is if in the country the language reading writing is in English how will the school that is mostly in a foreign language educate a child in English that is necessary they know

If anyone has attended or has children enrolled in a language immersion school could you let me know how they are doing with English